As one method for controlling an internal combustion engine, torque demand control is known that uses torque as a control amount for determining an operation amount of each of different actuators. A target torque that serves as a target value of a control amount is determined based on a torque requirement from a driver, which may be estimated from an accelerator pedal operation, or a torque requirement from a vehicle control device such as a VSC and a TRC. With an internal combustion engine having an established target air-fuel ratio, such as a gasoline engine, a target air quantity is determined from the target torque and a specific actuator for controlling the air quantity is operated according to the target air quantity.
The torque demand control described above may be applied to an internal combustion engine having a turbocharger or a mechanical supercharger. Some such supercharged internal combustion engines can actively control a boost pressure. For example, an internal combustion engine disclosed in JP-A-2006-242062 includes a turbocharger with an electric motor. Active control of the boost pressure is enabled by letting the electric motor assist in rotation of a compressor. An internal combustion engine disclosed JP-A-2007-056697 includes a turbocharger with a waste gate valve, in which the active control of the boost pressure is enabled by operating the waste gate valve to thereby increase or decrease a flow rate of an exhaust gas flowing into a turbine. Alternatively, the boost pressure may be actively controlled using an air bypass valve or a variable nozzle in a turbine. In the torque demand control performed in the internal combustion engine capable of such a boost pressure control, a target air quantity and a target boost pressure are determined from the target torque and the actuator for controlling the boost pressure is operated according to the target boost pressure, as disclosed, for example, in JP-A-2006-242062. To determine the target boost pressure from the target torque, a map may be used that represents measurements taken of boost pressures required for achieving different torque values variable according to different operating conditions.
As a method of vehicle control, a method for damping vehicle body sprung vibration or, in particular, pitching vibration through torque control for the internal combustion engine is known. The torque control for the internal combustion engine for this specific purpose will hereinafter be referred to as vehicle vibration damping control. In the vehicle vibration damping control, pitching vibration according to a current driving force is obtained from a vehicle body vibration model and high-frequency torque to cancel the pitching vibration is calculated. This damping high-frequency torque component is added to low-frequency torque calculated based on an accelerator pedal operation amount. A sum of the high-frequency torque component and the low-frequency torque component is then set as a target torque to thereby perform the torque control for the internal combustion engine.
For the vehicle vibration damping control in the internal combustion engine capable of controlling the boost pressure, a target boost pressure is determined based on the target torque that contains the high-frequency torque component for damping purpose. Since the high-frequency torque component contained in the target torque is directly reflected in the target boost pressure, the target boost pressure for performing the vehicle vibration damping control contains a high-frequency pressure component. In this case, an actuator for controlling the boost pressure is operated such that the boost pressure is vibrationally varied according to the target boost pressure containing the high-frequency pressure component.
A response lag, however, exists in an actual boost pressure relative to the operation of the actuator. The lag time in response involved herein is not so small as to be negligible as compared with a cycle of vibration in the vehicle vibration damping control. As a result, a phase shift that is not negligible occurs between the target boost pressure and the actual boost pressure as shown in the lower graph of FIG. 15. The phase shift between the target boost pressure and the actual boost pressure creates a situation in which the actual boost pressure is lower than the target boost pressure, specifically, the boost pressure is insufficient. In throttle operation based on the target air quantity, a throttle opening required for achieving the target air quantity is calculated based on the actual boost pressure. In this case, if the actual boost pressure is higher than the target boost pressure, the target air quantity can be achieved by reducing the throttle; however, if the actual boost pressure falls short of the target boost pressure, the target air quantity cannot be achieved by simply adjusting the throttle opening. This is because of the reason that a maximum value of the quantity of air to be drawn into a cylinder depends on the actual boost pressure and, and if the actual boost pressure falls short of the target boost pressure, the maximum air quantity becomes smaller than the target air quantity. As shown in the upper graph of FIG. 15, therefore, torque to be actually achieved yields a waveform different from a waveform of the target torque, so that it becomes impossible to give vibration required for damping the vehicle to the torque.
As described above, in the supercharged internal combustion engine including a boost pressure control actuator, such as a waste gate valve, the boost pressure can be actively controlled according to the target torque. Because of the response lag involved between the target boost pressure and the actual boost pressure, however, if target torque contains a high-frequency vibration component, the target torque may not be accurately achieved.